The lithium-ion battery has many advantages, such as its small size, high energy density, high cycle life, low self-discharge rate and no memory effect. Increasingly it has been used broadly as a major power device for mobile phones, notebook computers, digital cameras, electric cars and other products. Lithium-ion battery, however, is susceptible to damage and may catch fire if used improperly such as in case of overcharging or short circuits. Protective devices have been known for many years for detecting and preventing battery damage caused by such external factors, e.g., short circuits or overcharging. However, even in the course of normal use, lithium-ion batteries may develop side reactions in its internal electrochemical reactions, especially in the process of charging and discharging the battery. Such abnormal internal conditions may seriously affect the battery performance and its life. They also may produce large amounts of gas and cause the battery internal pressure to increase rapidly, leading to explosions and fires. It is thus desirable to use a protective circuit to monitor the charging and discharging of lithium-ion batteries to prevent the development of the abnormal internal conditions.